1. Field of the Invention
This invention relates to surgical cutting instruments. More particularly, this invention relates to novel surgical cutting heads or tips for performing surgery on various parts of the body, such as menisci (fibrous cartilages) located in body joints, e.g., knees, elbows and shoulders, or to remove malignant or nonmalignant fibroids or similar tissues through small bodily incisions from various parts of the body, and especially for use in infusion/aspiration devices for surgically removing cataractous tissue from the eye. The surgical cutting instruments of this invention will be described here with particular reference to their use in performing cataract surgery.
The eye's lens, a tough, almost completely transparent biconvex structure suspended behind the iris, is made up of an elastic capsule filled with cellular tissue. The lens adjusts the focusing of the eye when its shape is changed by the muscles of the ciliary body, to which the lens is connected by the zonular fibers.
The lens is susceptible to cataract formation--changes in the lens which make it opaque and which may hinder or destroy a person's vision depending on the cataract's size, shape and location. Cataracts can be congenital. They can also be caused by degenerative changes in the lens as a person grows older (senile cataracts). And, cataracts can result from trauma from accidents involving the eye, or from overexposure of the eye to heat, X-rays, ultraviolet rays or radioactive materials, or as a secondary effect of intraocular or systemic diseases, such as diabetes, or from exposure to various drugs. Cataracts can be cortical, involving largely or exclusively changes in the outer portion of the lens, or dense nuclear, involving primarily changes deep in the lens's interior, or can involve most if not all of the lens's proteinaceous material.
Treatments for cataracts generally involve removal of all or part of the lens through a small surgical incision (generally from about 3 to about 9 mm in length in the normal human eye, so that any instrument used during surgery can be inserted and removed without stretching the eye's tissue) made in the limbus, the portion of the sclera adjacent the cornea. Common practice has ordinarily involved then replacing the lens with a synthetic intraocular lens, or using a contact lens or a thick eyeglass to function as did the lens. Intracapsular cataract extraction ("ICCE") involves removal of the lens and the entire capsule. This technique is no longer in common use, except for subluxated lens and ocular trauma where the capsule or zonules are badly damaged. When extracapsular cataract extraction ("ECCE") is performed, a 4 to 7 mm portion of the anterior capsule and the lens's nucleus are removed, leaving the posterior capsule behind.
The main thrust of more modern cataract surgery has been towards smaller limbal incisions and less invasive approaches. Indeed, the success of the newest techniques now being developed to preserve and restore accommodation (the eye's ability to focus properly), such as refilling the entire lens with a synthetic substance once cataractous material has been removed, will depend upon the development of new instruments that can remove cataractous materials, including cataractous nuclei, through the smallest possible hole made at the periphery of the lens capsule. The present invention provides such instruments.
2. Description of the Prior Art
Cutting instruments disclosed in the prior art as being useful in cataract surgery include, inter alia, the upper and lower jaw member-containing cutting devices and rotating cutters disclosed in Banko U.S. Pat. Nos. 3,732,858 and 3,996,935, issued May 15, 1973 and Dec. 14, 1976, respectively, and the cutting devices disclosed in Hadded U.S. Pat. No. 4,320,761, issued Mar. 23, 1982, and Akkas, et al U.S. Pat. Nos. 4,909,249 and 4,986,827, issued Mar. 20, 1990 and Jan. 22, 1991, respectively.
Douvas, et al. U.S. Pat. Nos. 3,882,872 and 3,990,453, issued May 13, 1975 and Nov. 9, 1976, respectively, disclose infusion/aspiration cutting instruments useful in cataract surgery. In particular, the cutting heads or tips in the '872 patent's devices can comprise, first of all, a generally square or rectangular cutter bar fixed radially across the far end of a rotatable tube positioned inside another tube which also has a generally square or rectangular bar recessed and fixed radially across its far end; see FIG. 5 and from column 5, line 43 to column 6, line 2 of the '872 patent's specification. In another embodiment, the edge of the '872 patent's outer tube's far end can be curled inwardly to overhang the cutter bars; see FIG. 6 and column 6, lines 3-21. In a third embodiment as described in FIGS. 7 and 8 and at column 6, lines 22-45 of the '872 patent, the outer tube's far end is closed completely and the outer tube itself has a reduced bore for a distance from its proximal end so that it and the inner, rotatable tube fit closely together over that distance. The outer tube also has a pair of radial holes in proximity to its far end whose sharp edges, in conjunction with the sharp edges of an approximately 180.degree. straight edged wall segment at the far end of the rotatable inner tube, provide cutting edges for shearing off cataractous lens material drawn through these holes. See also FIGS. 11, 14-16 and 18-25 of the '872 patent.